1. Field of the Invention
The present invention relates to a process for producing a component, in particular a component for a turbomachine, for example an aircraft engine, composed of a high-temperature material, in particular a TiAl alloy.
2. Discussion of Background Information
The operation of turbomachines requires, owing to the use conditions of the components employed with sometimes high temperatures, aggressive environments and high forces acting on the components, specific materials for particular components, which materials are optimally matched to the use both in terms of their chemical composition and also their microstructure.
Alloys based on intermetallic titanium aluminide compounds (TiAl alloys) are used in the construction of turbomachines such as stationary gas turbines or aircraft engines, for example as material for turbine blades, since they have the mechanical properties required for this use and additionally have a low specific gravity, so that the use of such alloys can increase the efficiency of stationary gas turbines and aircraft engines. Accordingly, there are already many TiAl alloys and processes for producing corresponding components therefrom.
Components made of TiAl alloys can, like comparable components composed of other high-temperature alloys, for example alloys based on Ni, Fe or Co, be produced both pyrometallurgically and powder-metallurgically.
In pyrometallurgical production, the alloy used for producing the component is provided in the form of a melt and this is cast into a mold. The cast material usually has to be subjected to suitable deformation operations and/or heat treatments in order to destroy the cast microstructure and obtain a desired microstructure of the material. The corresponding component can then be brought to the desired shape by suitable after-working, for example by cutting machining or electrochemical working.
In powder-metallurgical production, the production steps comprise, in addition to or as an alternative to the individual steps of pyrometallurgical production, the use of powder materials in order to produce a desired composition of the material, for example by mechanical alloying. An example of the production of an object composed of a TiAl alloy using powder materials is described in U.S. Pat. No. 5,424,027, the entire disclosure of which is incorporated by reference herein.
According to this document, objects composed of TiAl alloys comprising 50 at. % of aluminum and also alloys comprising 48 at. % of aluminum and 1 at. % of niobium, 48 at. % of aluminum, 2 at. % of niobium and 2 at. % of chromium and also 48 at. % of aluminum, 1 at. % niobium and 1 at. % of vanadium and 48 at. % of aluminum, 3 at. % of niobium, 2 at. % of chromium and 1 at. % of manganese and in each case titanium as balance are produced by introducing an appropriately prealloyed TiAl powder into a suitable mold in order to be hot isostatically pressed subsequently. After hot isostatic pressing, the material is subjected to hot forming in order to produce a fine, uniform and isotropic microstructure.
For hot forming, which can be carried out both in pyrometallurgical production and in powder-metallurgical production as described in U.S. Pat. No. 5,424,027 or has to be carried out in order to achieve particular properties, a high outlay in respect of the hot forming steps is necessary. In addition, such a production method is associated with a high consumption of materials since near-net-shape production, for example by near-net-shaped casting, is not possible. In this context, there is then a further, increased outlay for cutting machining or electrochemical shaping of the component.
In view of the foregoing, it would be advantageous to have available a process for producing a component composed of a high-temperature alloy, in particular a TiAl alloy, by means of which a component can be produced efficiently with a reduction of the outlay compared to the prior art, with the material of the component having an optimal microstructure, in particular a homogeneous and uniform microstructure, so that the component likewise has uniform mechanical properties. The corresponding process should be able to be carried out simply and reliably and reproducibly allow suitable microstructures of high-temperature alloys and in particular TiAl alloys to be set so as to provide the required properties, in particular for components of turbomachines.